linux-kernel - Re: [PATCH 3/4] rtla/timerlat: Add example for BPF action program

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Message-ID: <ecedb0d1f2d0e51c56e462adf75df47e8d593a8c.camel@redhat.com>
Date: Thu, 23 Oct 2025 20:49:02 -0500
From: Crystal Wood <crwood@...hat.com>
To: Tomas Glozar <tglozar@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, LKML
 <linux-kernel@...r.kernel.org>,  Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, John Kacur <jkacur@...hat.com>, Luis
 Goncalves	 <lgoncalv@...hat.com>, Costa Shulyupin <costa.shul@...hat.com>,
 Wander Lairson Costa <wander@...hat.com>, Arnaldo Carvalho de Melo
 <acme@...nel.org>
Subject: Re: [PATCH 3/4] rtla/timerlat: Add example for BPF action program

On Thu, 2025-10-23 at 09:27 +0200, Tomas Glozar wrote:
> út 21. 10. 2025 v 19:32 odesílatel Crystal Wood <crwood@...hat.com> napsal:
> > 
> > On Tue, 2025-10-21 at 13:02 -0400, Steven Rostedt wrote:
> > > 
> > > Note, trace_array_printk() (which trace_array_init_printk()) only works for
> > > instances and does not print into the top level trace buffer.
> > 
> > Yes, it's for instances, such as the ones rtla creates.
> > 
> > -Crystal
> > 
> 
> Right, it actually works with the trace instance, when set up properly:
[snip]
>  Saving trace to timerlat_trace.txt
>     timerlatu/0-47791   [000] ...22 863353.286497: bpf_trace_printk:
> Latency: 21282

OK, but as far as I can tell there's no way to get the non-BPF "stop
tracing hit" messages without adding a call to trace_array_init_printk()
into trace_osnoise.c.

-Crystal